The present invention relates generally to the field of multiplexers and also generally to the field of mode suppression mechanisms. More particularly, the present invention relates to channelized down converters and to mechanisms for suppressing spurious propagation modes in the vicinity of 90.degree. suspended substrate hybrid couplers.
Channelized down converter techniques are finding increased use in surveillance receivers, especially at millimeter-wave frequencies where extremely wide bandwidths must be covered. Wideband mixers with switched or swept local oscillators have been used, but these systems are limited to an instantaneous bandwidth equal to the down converted IF bandwidth and also suffer from lack of image rejection. The key front-end component of the channelized down converter is the RF multiplexer. Millimeter wave multiplexers have been demonstrated previously in microstrip and finline structures. A major problem with these prior art fin line multiplexers has been the large amount of space required by them.